It’s not difficult to gauge the value Daniel Nava has provided the worst-to-first Red Sox this season. He is fifth in the American League with a .392 on-base percentage and third among AL outfielders with an .844 OPS.

But Nava’s hidden worth to the Sox and manager John Farrell has come on defense.

Nava has started 53 games in left field, 44 in right, eight at first base, and one in center field along with five starts as the designated hitter. No other player on the team has filled more positions.

Nava also has switched positions during a game 24 times. On 10 of those occasions, he played first base and the outfield.

Nava did the defensive cha-cha-cha Sept. 8 against the Yankees, going from right field to first base and then back to right field. His ability to move around the field has allowed Farrell more opportunities to get his bat in the lineup.

“That adds so much freedom to the decision-making at the moment,” Farrell said. “We can use Daniel as the safety valve.”

Nava is sixth on the team with 493 plate appearances this season despite not leading any one defensive position in starts.

Once he’s in the lineup, Nava has batted in eight spots in the order, everywhere but fourth. He and Shane Victorino are the only players on the team with at least three sacrifices and 11 home runs.

“In terms of roster structure, it’s almost like having two players because of what he’s capable of,” Farrell said.

Nava didn’t intend to become a super utility player, no player does.

But he quickly came to realize that it was the best path to getting to the plate.

Former Red Sox infielder Nick Punto advised Nava last season to get comfortable in more positions.

So when the Red Sox approached him in the offseason about playing first base, Nava welcomed the idea.

“This works for me,” said Nava. “It gives me the opportunity to play more and gives the staff more flexibility as far as lineup possibilities. You want to be part of a solution.”

Nava said the preparation is more mental than physical. He carries a cheat sheet in the back pocket of his uniform pants as a reminder of where to play certain hitters. At first base, he relies on instructions from second baseman Dustin Pedroia or the coaches in the dugout.

Nava said there have been a few plays in the outfield this season when he should have been better-positioned to make a play and it cost the team a run.

“It’s a little frustrating from my perspective,” he said. “I want to hold myself to a high standard and I think I haven’t focused as well as I should on some situations. It’s something that bothers me.

“But overall, in terms of the improvement from when I first came up, it has been pretty good.”

Nava is a switch hitter but has only 124 plate appearances righthanded. Farrell has been careful to put Nava in positions to succeed and give him regular days off.

“Over the past couple of years, the one thing we’ve had to balance is stamina, particularly at this level,” Farrell said. “He’s grown into that and understood the expectations at the big league level and what it takes to compete.”

When Farrell was named manager last year, he told general manager Ben Cherington that he felt Nava could help the team. The Sox sent minor league instructor Andy Fox to Arizona during the winter to work with Nava on playing first base. That picked up intensity during spring training under infield coach Brian Butterfield.

By the time the season started, Nava was an important piece of the roster.

“We felt like there was potential there,” Cherington said. “He’s always had the ability at the plate and John felt we could try him in different spots. He became a better asset. The ability to play different positions allows John to match up more.”

Cherington then laughed.

“Bill Belichick would love him because he can play different positions,” he said.

Farrell was with the Red Sox as pitching coach when Nava made his debut in 2010. He saw something in Nava then that stuck with him.

“It’s important for us that we can never fully measure what’s inside a given player,” he said. “You never give up on a guy who shows you some talent. If given enough opportunity and time, they can overcome some things.”

Nava was 4 for 5 with two doubles and an RBI in Sunday’s 9-2 victory against the Yankees. In 15 games against them this season, Nava hit .375 with seven extra-base hits, seven runs, and 10 RBIs.

Fatherhood also agrees with Nava. He has hit .400 with a 1.051 OPS in 28 games since the birth of his daughter, Faith, in August. Perhaps new mom Rachel Nava should get a playoff share.

Nava’s compelling back story — he was cut from his college team, became the equipment manager, then made his way to the majors via junior college and independent ball — has faded into the background.

The grand slam he hit in his first at-bat back in 2010 did not prove to be the highlight of his career.

Nava is now a productive everyday player for the best team in baseball.

“It’s a guy you root for,” said Farrell. “This is a story like no other in the game. To perform at the level he is right now, this is something nobody would ever foresee. With the work he’s put in, he’s deserving of all the credit that comes his way.”

Red Sox bench coach Torey Lovullo asked Nava a few days ago if he ever thought he would be in this position a few years ago. “I told him, ‘Never. No way,’ ” said Nava. “I was going one day at a time.

“But that was a good way for me to look at things, to just play that day. I feel very blessed. I think after the season I can look back and reflect.

“I feel like I’m a reflection of this team in some ways. We have a lot of balance and a lot of guys who pick each other up. That’s the beauty of this team, we can relax and go out there and have fun.”

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